SCOPE OF DIAGNOSTIC IMAGING
CHAPTER 1
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using diagnostic techniques such as magnification and/or spot compression views may also be obtained to further characterize potential pathologic findings. Ultrasonography (US) is also used in breast imaging as a complementary modality to further characterize breast pathology. Several imageguided breast interventional procedures, such as preoperative needle placement for lesion localization and core needle biopsy using stereotactic ultrasound or MR guidance, are widely available.
Contrast Studies Contrast materials are used to examine organs that do not have natural inherent contrast with surrounding tissues. Contrast media are commonly used to evaluate the gastrointestinal tract, the urinary tract, the vascular system, and solid organs. Contrast media used in MR imaging are described in the MR modality section. Barium suspension is still used daily in the examination of the gastrointestinal tract. Barium suspension is a safe contrast media that provides high imaging density on upper gastrointestinal (UGI) series, small-bowel studies, and evaluation of the colon. Both single-contrast and doublecontrast techniques may be used to evaluate the gastrointestinal tract (Figure 1-2). In the single-contrast study, barium suspension is administered alone. In the doublecontrast study, both barium and air are introduced to delineate the details of the mucosal surface, which facilitates the identification of superficial lesions in the bowel lumen. In the UGI double-contrast study, air is introduced into the bowel lumen by administering oral effervescent agents. For double-contrast evaluation of the lower GI tract with barium enema, air is introduced into the bowel lumen via direct inflation with a small pump through a rectal catheter. Small-bowel contrast studies include peroral, enteroclysis, and retrograde techniques. The peroral small-bowel study is performed by feeding barium suspension to the patient and recording the progress of contrast through the small bowel. Enteroclysis is performed by placing a catheter in the proximal jejunum and infusing barium suspension through the catheter. Enteroclysis is preferred for evaluating focal small-bowel lesions or the cause of small-bowel obstructions. Retrograde small-bowel examination is performed by retrograde reflux of barium suspension into the small bowel during barium enema or via direct injection through an ileostomy. Water-soluble contrast media are commonly used for angiography, interventional procedures, intravenous urography, and enhancement of CT. All water-soluble contrast media are iodinated agents that are classified as high or low osmolar, ionic or nonionic, and monomeric or dimeric in chemical nature. The iodine atoms in contrast medium absorb x-rays in proportion to the concentration in the body when radiographed. The most common water-soluble contrast
Figure 1-2. A single-contrast retrograde colonic enema in the left posterior oblique view demonstrates an annular lesion representing a cecal carcinoma (arrows). Bilateral hip prostheses are an incidental observation.
media are the high osmolar ionic contrast agents (diatrizoate and its derivatives). Low osmolar contrast media include ionic (meglumine ioxaglate) and nonionic (iohexol, iopamidol, ioversol, iopromide) monomers, as well as nonionic dimers (iodixanol). Low osmolar contrast media have an overall lower incidence of adverse reactions, including nephrotoxicity and mortality, than high osmolar ionic agents; however, lower osmolar agents are also three to five times more expensive. The occurrence and severity of adverse reactions after administration of iodinated contrast material are unpredictable. These reactions are categorized as mild, moderate, or severe based on degree of symptoms. Mild adverse reactions include nausea, vomiting, and urticaria that do not require treatment. The incidence of mild adverse reactions may be less if using a lower osmolality contrast agent. Moderate reactions include symptomatic urticaria, vasovagal events, mild bronchospasm, and/or tachycardia that requires treatment. Severe and life-threatening reactions, such as severe bronchospasm, laryngeal edema, seizure, severe hypotension,
